Sound pressure level is the standard because it matches hearing

Evidence

These different means of describing and measuring sound amplitudes can be confusing, and one must be careful to ascertain which one is being used in a given context. In general, a reference to sound level implies that the SPL is being used because the pressure component can be measured easily and corresponds most closely to what we hear. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 211

Categorization

• DEFINE: Explains why SPL is the default when people say ‘sound level’ — a useful field-terminology anchor.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 211
• XREF: connects to: At equal A-weighted level, railway noise is judged quieter than road and aircraft noise — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1812; Logarithmic hearing means equal decibel steps need larger absolute pressure differences; Sound level references implicitly mean sound pressure level (+2 more)

Broader Connections

• Sound level references implicitly mean sound pressure level #expands (0.82)
• Measurable and audible sound qualities can be shown to correlate reliably #exemplifies (0.72)